For ascertaining or monitoring a physical or chemical process variable, the most varied types of sensors are used, which can function on the basis of very different physical principles of measurement. Thus, for example, the fill level of a fill substance in a container can be measured via the travel time of ultrasonic waves or electromagnetic waves, especially microwaves, which are reflected on the surface of the fill substance. In the case of microwaves, these are either radiated freely into the container in the direction of the surface of the fill substance, or they are guided along a conductive element into the container.
Beyond this, capacitive and radiometric measuring methods are used for fill level measurement. For limit level detection, preferably the resonance frequency of an oscillatory rod or an oscillatory structure made of a plurality of oscillatory rods is evaluated. In this method of measurement, one evaluates resonance frequency changes based on transitions between when the oscillatory rods are executing their oscillations freely and when such is occurring under contact with the fill substance.
Other process and controlled variables ascertained and monitored in process automation and measurements technology are, for example, temperature, pressure, ion-concentration, conductivity and flow, e.g. flow rate, of a medium through a pipeline. Of great importance in this connection are display or registering devices (display units), on which information won in the measurement is displayed, so that, at any time, the current state of a monitored process is available for operating personnel. Measuring devices and display devices of the above-described kind are sold by the Endress+Hauser Group in a multitude of variants optimally adapted to given processes.
The representation on the display of a display/registration device (display unit) should, of course, be matched as optimally as possible to the particular application; it is desirable, in this respect, that a quick glance at the display of the display unit can already deliver a clear indication what is happening in the particular application. For example, a process can be designed such that a tendential increase, or rise, of a measured variable is to be expected, such as would be the case e.g. in the filling of a container. The opposite situation arises in the emptying of a container, e.g. in a so-called “well application”. Different again is the case involving control of a process variable to a predetermined setpoint—here, mainly the deviation of the currently measured process variable from the predetermined setpoint is of interest. It would thus appear to lie in the nature of the matter that, for these different applications, the suitable display equipment would likewise need to be designed differently.